1. Field of the Invention
This invention relates to a method for the growth of a semiconductor single crystal by causing a seed crystal to contact a molten semiconductor in quartz crucible and pulling up a rod of semiconductor single crystal. More particularly, this invention relates to a method for the growth of a semiconductor single crystal, characterized by imparting a prescribed distribution to the oxygen concentration of the semiconductor single crystal in the direction of length of pull-up thereof by the adjustment of the intensity of a magnetic field applied to the molten semiconductor.
2. Description of the Prior Art
In the growth of a single crystal of silicon by the Czochralski method, a quartz (SiO.sub.2) crucible is used as a container for holding molten silicon. It is known that since silicon at the melting point thereof is chemically active, the molten silicon reacts with the quartz of the crucible and dissolves the quartz into itself and, as a result, the grown single crystal of silicon contains a fair amount of oxygen. At the same time that the quartz glass of the crucible dissolves into the molten silicon, the trace of impurities present in the shell of the crucible are dissolved and eventually incorporated in the grown single crystal of silicon.
The oxygen of the single crystal of silicon is welcomed on account of the so-called intrinsic gettering effect. Techniques for uniformly distributing oxygen on a relatively high level, a level on from 15 to 20 ppma, for example, throughout the entire length of the single crystal of silicon have been developed. Japanese Patent Publication SHO 60(1985)-6,911 and Japanese Patent Application Disclosure SHO 57(1982)-135,796, for example, disclose such techniques. In consequence of the advance of the technology for the manufacture of integrated circuits, the demand for the intrinsic gettering effect has dwindled and, at the same time, the demand for a single crystal of silicon containing impurities other than oxygen in the smallest possible concentration has grown. The trend has urged development of a method for producing a crystal of high purity by applying a magnetic field to molten silicon thereby curbing the melt of the raw material for the crystal from undergoing convection and consequently repressing the dissolution of the quartz glass of the crucible. One technique for embodying the method is disclosed in Japanese Patent Application Disclosure SHO 56(1981 )-104,791, for example.
Japanese Patent Publication SHO 60(1985)-6,911 discloses a method which, in the process for pulling up a rod of a single crystal from the melt of the raw material for semiconductor held in a quartz glass crucible in accordance with the Czochralski method, controls the gradient of the speed of revolution of the crucible so as to be reciprocal to the gradient of the oxygen concentration profile measured along the direction of pull-up.
Japanese Patent Application Disclosure SHO 57(1982)-135,796 discloses a method which comprises pulling up a grown seed crystal of silicon while rotating it in the direction opposite that of the rotation of the crucible for the melt at a large initial speed of revolution and further increasing the speed of revolution in proportion as the amount of the melt in the crucible decreases.
Japanese Patent Application Disclosure SHO 56(1981) -104,791 discloses a method for producing a crystal of high purity by applying a magnetic field to the raw material for the crystal thereby curbing the melt from undergoing convection and consequently repressing the dissolution of the quartz glass of the crucible.
None of the techniques described above, however, contemplates repressing the oxygen concentration in the grown single crystal to a low level even below 10 ppma, for example, throughout the entire volume of the rod of single crystal, uniformizing the distribution of oxygen concentration from the head to the tail of the rod of crystal, or controlling the distribution arbitrarily.